I have a Rails 4.1 application with nginx and unicorn. Some of POST request are turn into GET request. I gues it\'s related my nginx config. Here is the previous question ab
You may also want to try a 307 redirect. I found that my POST's were turning into GET's with the 301 redirect.
I.e. your server block becomes:
server { server_name www.my-app.com my-app.com; return 307 $scheme://$host$request_uri; }